In the recovery of oil and gas from subterranean hydrocarbon formations, it is common practice to stimulate or fracture the hydrocarbon-bearing rock formation, providing or enhancing flow channels for oil and gas. These flow channels facilitate movement of the hydrocarbons into the wellbore so they may be produced from the wellbore. Without fracturing, many wells would not be economically viable.
In such fracturing operations, a fracturing fluid is injected down a wellbore penetrating the hydrocarbon formation. The fracturing fluid is forced down an annulus of the wellbore and into the formation strata or rock under pressure, forcing the rock to crack apart. Various methodologies are known for stimulating formations in horizontal or vertical open hole completion. One such methodology is a Source MultiStim™ system employing a multi-stage cased/open hole hybrid system that sets up wellbore isolation and frac points along an open hole section of the wellbore. A MultiStim™ frac liner and packers are run into an open hole for isolating a series of zones. Each zone can be stimulated in sequence accessed through a series of open/close sleeves in the liner. Each sleeve for each zone is shifted of actuated using a dropped ball to open a port to the formation. After a zone is fractured using high pressure fracturing fluid, a successive ball is dropped to actuate the next uphole sleeve and the process is repeated. At the completion of the stimulation, retrieval of all balls enables full bore access to the liner for production of hydrocarbons from the formation.
However, use of ball actuation can be problematic for several reasons including the need for retrieval of the balls using a retrieval string, ball loss or ball injection failure among others. Further, for fracturing treatment of tight rock formations, such as those found in the Cardium Formation of West Central Alberta, it can be difficult to cause an initial break down of the rock formation. Thus, in particularly hard rock formations, formation strata may not readily crack or fracture merely with the application of high pressure fluids. Such tight rock formations can require higher fracturing pressures than that which can be supplied by surface equipment of a conventional fracturing or completion string. In such cases, perforation guns are sometimes required in advance of treatment. Perforation guns require additional equipment and time consuming and expensive runs in and out of the wellbore.
Accordingly, there is still a need for reliable access to the formation and means for dealing with difficult formations.